Q: example of undefined terms

A: POINT (an undefined term)
In geometry, a point has no dimension (actual size). Even though we represent a point with a dot, the point has no length, width, or thickness. A point is usually named with a capital letter. [ In the coordinate plane, a point is named by an ordered pair, (x,y).
LINE (an undefined term)
In geometry, a line has no thickness but its length extends in one dimension and

goes on forever in both directions. A line is depicted to be a straight line with two arrowheads indicating that the line extends without end in two directions. A line is named by a single lowercase letter, , or by two points on the line, .
PLANE (an undefined term)
In geometry, a plane has no thickness but extends indefinitely in all directions. Planes are usually represented by a shape that looks like a tabletop or wall. Even though the diagram of a plane has edges, you must remember that the plane has no boundaries. A plane is named by a single letter (plane m) or by three non-collinear points (plane ABC). ]

Expert answered|phobicism|Points 2049|

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Asked 6/16/2010 4:19:43 AM

Updated 6/16/2010 7:07:52 AM

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There are a few basic concepts in geometry that need to be understood, but are seldom used as reasons in a formal proof.

Collinear Points points that lie on the same line.

Coplanar points points that lie in the same plane.

Opposite rays 2 rays that lie on the same line, with a common endpoint and no other points in common. Opposite rays form a straight line and/or a straight angle (180°:).

Parallel lines two coplanar lines that do not intersect

Skew lines

two non-coplanar lines that do not intersect.